wildbill:
The majority of arduino projects you'll see on the forum run continuously, sensing something and acting on it. Some of course do have a definite end - beer brewing would be an example. Purely out of curiosity, what are you making?
My wife's car has Push-To-Start ignition and as of right now there are no Immobilizer bypass or remote start solutions for it, so I'm creating one.
I have a remote start already, and an extra key-fob. I want to use the arduino to sense the remote start having been activated. Once 'activated' it will power on a burried key-fob so that the key information is radiated via RF into the car allowing engine startup. Next it will power up the brake circuit to simulate pressing in the brake pedal. The Arduino will then pulse the PTS button to fire up the engine, shutting off the key-fob afterwards preventing someone from getting into the vehicle and driving off with it. (the next part is the reason for wanting to end the program)
At this point the arduino will monitor the remote start's Status wire (shows ground when running, and floats high when off). If the Status wire drops ground it will pulse the PTS button twice to shut off the engine, and then pulse the driver's door pin wire to turn off the dome lights preventing battery drain. This is essentially to shut off the vehicle should the remote start time-out.
If the Arduino instead sees the brake pedal being pressed while the remote start is still running, it will not pulse the PTS button but will power off the remote start via the Brake Pedal Input sensing wire on the remote start. This will essentially allow key takeover.
Hope all that made sense 